Since the widespread adoption of the Montreal Protocol, the urethane industry has concentrated efforts directed to eliminating the use of chlorofluorocarbons, such as the widely used CFC-11, from polyurethane foam formulations of all types. The use of HCFC's such as HCFC-22, monochlorodifluoromethane, which have lower ozone depletion potentials (ODP's) has been promoted as an interim solution. However, HCFC-22, an HCFC of choice, is a gas at room temperature with poor system solubility, and thus extraordinary processing equipment must be used, including in some cases, pressurized day tanks.
Water has been utilized for many years in polyurethane and polyisocyanurate foam systems. However, the carbon dioxide generated by the water/isocyanate reaction is markedly inferior to the CFCs and HCFCs with respect to preparing rigid foams having low K-factors. To overcome this deficiency, it has been suggested to include perfluorocarbons (PFAs) in a water blown formulations. However PFAs are quite expensive despite being used in modest amounts; have exceptionally poor system solubility, often requiring emulsification rather than solution; and moreover offer only a modest advantage over all-water-blown systems.
Low-boiling aliphatic hydrocarbons have been suggested as blowing agents for polymeric foams, and are widely used in the expandable and expanded polystyrene industry. However, they have been eschewed by the polyurethane industry due to the flammability of the foams produced through their use, as well as the high K-factors obtained in rigid foams, making them undesirable for use in many applications.